The importance of rumen digestion of protein in the productive efficiency of ruminant diet formulations has been recognized for a considerable time. Feeds entering the rumen environment are digested with variable efficiency, such that the contribution of protein and energy to the rumen fermentation, or alternately to the animal via rumen escape followed by intestinal digestion and absorption, varies widely among feedstuffs. The variability in feeding value amongst feeds and animal classes has led to the development of diet evaluation software incorporating digestion rates relating to a variety of nutritionally important protein and carbohydrate fractions (Dairy NRC 2001; Fox, et al., 1992.).
As summarized in such computer programs, the specific feed value of a dietary ingredient varies both with animal productivity and diet formulation or composition. As animal productivity increases, so do the nutritional requirements for amino acids, metabolizable protein and energy. At low levels of production, nutrition demands are more readily satisfied by the end products of rumen fermentation, such as volatile fatty acids for energy, and microbial proteins to supply metabolizable protein and amino acids. At elevated production levels the gross efficiency of nutrient digestion decreases, increasing the proportion of nutrients escaping rumen fermentation. The specific efficiency of microbial protein produced in the rumen is somewhat variable and difficult to predict, but does not increase sufficiently, such that rumen fermentation is unable to supply the quantity of metabolizable protein required to meet productive demands. This shortfall of rumen microbial protein production increases the dietary demand for rumen bypass protein. Thus, research efforts aimed at achieving continued increases in ruminant productive level and efficiency have emphasized the importance of the nutrients which escape or bypass rumen fermentation. Therefore, a number of rumen escape proteins are now available in the marketplace.
A parallel development to rumen escape protein has been an increase in dietary energy density to meet the energetic demands of increased production. For high production situations, this has increased the level of rumen fermentable carbohydrate in diets by raising starch levels. Increased feeding of starchy ingredients has led to increased concerns relating to rumen acidosis and the resulting loss of rumen fermentation efficiency and animal productivity.
A variety of methods have been used to reduce the rumen availability of vegetable protein. U.S. Pat. No. 3,619,200 proposes a rumen-inert coating of vegetable meal for protection against rumen microbial digestion. Treatment of feeds with tannin, formaldehyde, or other aldehydes can denature the protein and reduce ruminal fermentation (see U.S. Pat. No. 4,186,213), and rumen digestion of protein can be reduced by heating (Tagari et al., Brit. J. Nutr. 16:237-243 (1982)).
Hudson, et al., J. Anim. Sci. 30:609 (1970) presents an experiment comparing evaluating the effect of heating on SBM on the post ruminal nitrogen utilization by lambs. The results indicated slower protein digestion by rumen microflora.
Endres, et al., 1996, and Heitritter, et al., 1998 (U.S. Pat. Nos. 5,508,058 and 5,824,355, with references) summarize the procedures commonly used for production of heat-treated vegetable meals.
The patents of Meyer, 1987, 1988, and Endres, et al., 1996 (U.S. Pat. Nos. 4,664,905, 4,664,917, 4,704,287, 4,737,365, 5,508,058) disclose the use of zinc salts to protect animal feed protein from rumen degradation.
The patents of Meyer, 1987 and 1988 (U.S. Pat. Nos. 4,664,905, 4,664,917, 4,704,287, 4,737,365) established the use of relatively high levels of zinc salts to improve protein utilization in beef and dairy cattle and sheep. Incorporation levels of zinc were from 0.25 to 1.3% dry weight or alternately 0.005 to 0.0294 parts zinc ion per unit protein in a protein dry blend.
Endres, et al., 1996 (U.S. Pat. No. 5,508,058) disclose a method to produce heat treated vegetable protein incorporating zinc at a lower level than previously discovered (0.003 to 0.008 parts zinc per part protein). As discussed in that disclosure, the use of lower zinc levels is beneficial in reducing the excretion of zinc into the environment via animal manure while retaining efficacy of reducing rumen protein digestion of the protein feed.